A pressure sensitive adhesive, generally, is a material which adheres to a surface with pressure and can release from a surface with negligible transfer of the material to the surface. Silicone pressure sensitive adhesives have been found to be preferred over other types of pressure sensitive adhesives in many applications, especially in the medical area. For example, silicone pressure sensitive adhesives, due to the fact that they are acceptable for topical use, have found use in transdermal drug delivery applications which involve the adherence and sealing of a drug-containing patch to a patient's skin.
However, many current silicone pressure sensitive adhesives experience a degree of "cold flow", that is, flowing or softening at temperatures near room temperature. The amount of cold flow is increased when the silicone pressure sensitive adhesive is in contact with a patient's skin, as the higher temperature of a patient's skin causes a further softening of the silicone pressure sensitive adhesive. Flowing or softening of the silicone pressure sensitive adhesive can cause shifting of the pressure sensitive adhesive on the drug-containing patch during storage or use which can decrease the efficacy of the drug-containing patch. There is, therefore, a need for a silicone pressure sensitive adhesive having a reduced propensity for cold flow.
U.S. Pat. No. 5,079,008 to Sinnreich et al. teaches a monolith transdermal therapeutic system for the delivery of permeable drugs, especially formoterol, in the form of a matrix system comprising three layers: a) a backing layer which is impermeable to the components of the adhesive layer b), b) an adhesive layer capable of releasing the drug and consisting of a permeable polymeric material which is compatible with the skin and contains at least one drug which is capable of permeation across the skin, a combination of eucalyptol having a purity of at least 70% with an additional flux enhancer and further optional pharmaceutical excipients, and c) a protective release liner which can be peeled from the adhesive contact layer b).
U.S. Pat. No. 5,176,915 to Hoffmann teaches a plaster used as therapeutic system for the administration of active substances to the skin exhibiting a graduated active substance release, to the process for the production of such a plaster, and to the use for the local or systemic dermal administration of active substances in the human or veterinary medicine, or in cosmetics.
U.S. Pat. No. 5,300,291 to Sablotsky et al. teaches a method of increasing the adhesiveness of a shaped pressure sensitive adhesive, comprising adding an adhesive and drug release increasing amount of a clay to said adhesive prior to casting of the adhesive. A dermal composition comprising a drug, a pressure sensitive adhesive, an adhesiveness increasing amount of a clay and a solvent. A dermal composition comprising a drug, a multipolymer of ethylene vinyl acetate, an acrylic polymer, a natural or synthetic rubber and a clay, along with optional ingredients know for use in transdermal drug delivery systems.
U.S. Pat. No. 5,342,623 to Enscore et al. teaches rate controlled transdermal delivery devices which utilize an in-line adhesive to maintain the device on the skin and deliver an agent which is a solvent or a plasticizer for the in-line adhesive. The initial equilibrated concentration of the agent in the agent reservoir and the adhesive is below saturation, and the reservoir comprises the agent dissolved in a solvent with respect to which the rate controlling element of the device is substantially impermeable. In preferred embodiments the initial loading of the agent in reservoir is sufficient to prevent the activity of the agent in the reservoir from decreasing by more than about 50% and preferably no more than about 25% during the predetermined period of administration; and the thicknesses of the adhesive, rate controlling membrane and reservoir layers are selected so that at least 50% and preferably at least 75% initial equilibrated agent loading is in the reservoir layer. The devices are usable to deliver agents which are liquid at body temperatures such as benztropine, secoverine, nicotine, arecoline, polyethylene glycol monolaurate, glycerol monolaurate, glycerol monooleate and ethanol, for example.
All of the aforementioned references teach pressure sensitive adhesives containing polyisobutylene polymers, but none teach the combination of polyisobutylene and silicone components.
Other desirable attributes of a pressure sensitive adhesive of this invention include the biocompatibility of the pressure sensitive adhesive to animal skin and the capability of (a) making the pressure sensitive adhesive hot-meltable, (b) modifying the properties of the pressure sensitive adhesive, such as drug permeability, solubility, adhesiveness, releasibility, and tackiness, and (c) making the pressure sensitive adhesive either transparent or white resulting in an aesthetically-pleasing product.